Maximum Line Pull or Rating This is the maximum effort that the winch can exert on a single line on the first layer of the winch drum. As the layers of cable build up on the winch drum, the overall cable speed increases, however the rated line pull decreases at the same rate. By using a snatch block to obtain a "double line pull" you can in effect almost double the pulling capacity of your winch, whilst approximatly halving the overall recovery speed. It is good practice to use a snatch block when performing a "heavy" self recovery as it will decrease the current running through your electric winch motor and help to prevent overheating and damage to the unit. How to work out the capacity of winch you need: Ideally the rating of your winch should be in excess of 1.5 times the gross weight of your vehicle. Put simply, a 2 tonne Land Rover should be equiped with a winch with a capacity of 3.5 Tonnes or greater. You can work out an approximate winch load for various types of self recovery using the following details: 1. Gross Vehicle Weight (Wt) 2. Surface Drag (S) | Surface Type | Metal | Sand | Gravel | Soft Sand | Mud | Marsh | | Surface Drag (S) | 0.15 | 0.18 | 0.20 | 0.22 | 0.32 | 0.52 |
3. Gradient Resistance (G) | Gradient | 5% | 10% | 20% | 30% | 50% | 70% | 100% | | Angle | 3º | 6º | 11º | 17º | 26º | 35º | 45º | | Value of G | 0.06 | 0.11 | 0.2 | 0.3 | 0.44 | 0.58 | 0.71 |
Use the following formula to calcluate the "Line Pull" required to recover a vehicle: Line Pull = (Wt x S) + (Wt x G) For example, if we take a 2 tonne Land Rover which is stuck in a sand dune of gradient 20% we would calculate the Line Pull required for recovery as follows: Wt: 2000Kgs S: 0.18 G: 0.2 Line Pull = (2000 x 0.18) + (2000 x 0.2) Line Pull = 360 + 400 Line Pull = 760Kg |